The present invention concerns testing equipment and methods for high-frequency devices, particularly test probes for wireless communications devices.
The increasing popularity of wireless communications devices, such as mobile telephones and pagers, has placed considerable demand on the limited range of broadcast frequencies that the federal government allots for these devices. In response, the federal government has extended this range to include higher frequencies. For example, the range for these devices now includes frequencies in the range of 27-32 Giga-Hertz. (A Giga-Hertz is one billion cycles or oscillations per second.)
In turn, makers of communication devices now offer or intend to offer devices that function at these higher frequencies. At the heart of many of these devices is a multi-tiered electronic assembly, which includes an integrated-circuit chip, a chip carrier, and a main circuit board. The chip is soldered onto one side of the larger, and sturdier, chip carrier. The other side of the chip carrier is soldered to the main circuit board, sandwiching the chip carrier between the chip and the main circuit board. The main circuit board, known as a motherboard, includes circuitry that electrically communicates with the chip through conductors inside and on the surface of the chip carrier.
One important aspect in making these multi-tiered electronic assemblies is testing their electrical capabilities. The conventional testing procedure tests each motherboard with the chip and chip carrier mounted to it. This testing, which is typically done manually, entails using test probes not only to apply test signals to inputs of the motherboard, but also to measure output signals at its outputs. A network analyzer, coupled to the test probe at the outputs, shows whether the output signals are acceptable or unacceptable. Unacceptable assemblies are generally discarded, because of the difficulty in salvaging the chip, chip carrier, or motherboard for reuse.
One conventional type of test probe that is considered suitable for testing high-frequency electronic assemblies is the ground-signal-ground (GSG) single or dual signal-port probe. This probe type places each signal probe tip between two grounded probe tips, which electrically shield the signal probe tip during testing. The ends of the ground and signal tipsxe2x80x94that is, the ends which contact the device under testxe2x80x94are substantially identical in structure, each having a sharp pointed end to facilitate its precise placement on conductive portions of the device under test. One example of this type probe is the PICOPROBE brand test probe from GGB Industries. (PICOBROBE appears to be a trademark of GGB Industries.) Another example is shown in U.S. Pat. No. 5,565,788.
There are at least two problems that the present inventors have recognized with high-frequency applications of conventional test probes and test methods. The first problem is that proper probe operation requires the device under test, such as a motherboard assembly, include at least two ground pads, or contacts, next to each signal port being tested. The ground contacts engage the ground probe tips at the sides of the signal probe tip to shield the probe from electrical interference during testing. However, at high frequencies, these adjacent ground pads can generate parasitic resonances which frustrate normal operation of the devices.
The second problem is that conventional test methods only test complete motherboard assembliesxe2x80x94that is motherboards with mounted chips and chip carriers. Because of the difficulty in separating chip carriers from motherboards, defective motherboard assemblies are discarded as waste, increasing manufacturing cost.
Accordingly, there is a need for better test probes and testing methods for high-frequency electronic assemblies.
To address this and other needs, the present inventors have devised unique test probes for testing high-frequency electronic assemblies, such as those for wireless communications devices. One unique probe structure includes at least one signal contact surface for contacting a signal-port trace of an electronic assembly and at least one ground contact surface for contacting a ground pad of the electronic assembly, with the ground contact surface substantially larger than the signal contact surface. Another unique probe structure includes at least one signal contact surface for contacting the signal-port trace and a ground probe having a contact surface for contacting the ground pad and a non-contact surface for overhanging a portion of the contacted signal-port trace and thereby establishing a characteristic impedance. Other unique probe structures include not only the larger ground contact surface or the ground with a non-contact surface, but also contacts for communicating electrical bias signals to devices under test.
Other aspects of the invention include systems and methods that incorporate one or more of unique probe structures. One exemplary system mounts one or more of the unique probe structures to a programmable XYZ table to facilitate rapid testing of chip-carrier assemblies. And, one exemplary method entails testing one or more millimeter-wave chip-carrier assemblies using a unique probe structure prior to mounting the assembly to a main circuit board, such as a motherboard.